One crucial function they perform is the formulation of business plans. This plan is based on the information provided by the client coupled with the vast wealth of knowledge and research a business plan consultant has.
U.S. Census Bureau (census.gov): A source for a variety of useful statistics, especially the Economic Census that comes out every 5 years.
Executive Summary - One to three pages that summarize all the information to follow; come back and write this last.
Introduction - What is the name and address of the business? Who are the principals, their titles, and their addresses? What is the nature or purpose of the business? What is your launch date? How much start-up and/or operating capital is needed?